<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <script>
        var str = 'abcdefg'
        var sum = str.split('')
        sum.reverse()
        var num = sum.join('')
        console.log(num)
    </script>
</body>

</html>